The invention relates to a method of manufacturing molded bodies or a granulate from calcium hydroxyphosphate and to the molded bodies and the granulate thus obtained.
Hydroxyphosphate is often used as an implantation body in dental surgery and orthopaedic surgery due to the fact that this compound exhibits an excellent bio-compatibility. A granulate of this composition is used in plastic surgery as a filler, for example, for correcting facial asymmetry.
A method of manufacturing these bodies is known from an article by G. de With c.s. in J. Mat Sci 16 (1981) 1592-1598. In accordance with this method a powdered calcium hydroxyphosphate [Ca.sub.5 (PO.sub.4).sub.3 OH] is isostatically pressed to form a body which is sintered in a water-vapour containing oxygen atmosphere at a temperature of 1200.degree.-1300.degree. C.
However, the body thus obtained has a blue colour, probably caused by impurities present in the starting material.
However, there are disadvantages attached to the presence of a blue color, in particular, when the application of the material is readily visible, such as with dental protheses. However, also in the case of invisible application in the human or animal body there is a psychological objection to the blue color as shown very different from the color of the natural bone.
It is an object of the invention to provide molded bodies and a granulate of hydroxyphosphate having a white color.
It has been considered to obtain this color by rigorously purifying the raw materials or hot pressing the material at a much lower temperature than the sintering temperature, but at high pressure, but these possibilities had to be abandoned because of the complexity and high cost of these operations.
In accordance with Japanese Patent Application No. 80/130 854 which is laid open to public inspection and to which reference is made in Chemical Abstracts 94 (1981), 179 537W, a white color is obtained by sintering the starting materials at a temperature of 1100.degree. C. or hot pressing at a temperature between 700.degree. and 1200.degree. C. in a flow of an inflammable gas mixture of H, CO, watergas and/or cracked NH.sub.3 -gas comprising water-vapour having a dew point of 5.degree. C. Heating in such an inflammable gas mixture is objectionable, however, due to the fire or explosion hazard.